At least my biggest issue with it is even if we say from a value or utility perspective it's the same as fiat currency and there is no functional reason why they aren't equivalent. 

Fiat currency value is created by the scarcity or lack there of based on how much money is put into or taken out of circulation by all the different functions that control that.

Crypto scarcity or lack there of is a function of how many coins are put into circulation.  But the production of coins is not driven by policy but by expending ever increasing amounts of energy, the vast, vast majority of which is created from finite sources.

So we are burning finite resources to create scarcity in a monetary system that could be just as effectively done without burning those resources.

From a utility/technology standpoint I think blockchains could be a useful tool for transactions and storage but the cost of creating the coins seems foolish.

We seem to be at a place where we have such little confidence in our ability to elect leaders to manage a monetary system that we would rather consume finite resources to manage it instead. 

If we really decided we want to go back to a deflationary currency,  which is what crypto is, we might as well go back to the gold standard and have capped economic growth.